In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date part of common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned.
Mass spectrometers are specialist devices used to measure or analyse the mass-to-charge ratio of charged particles for the determination of the elemental composition of a sample or molecule containing the charged particles.
A number of different techniques are used for such measurement purposes. One form of mass spectrometry involves the use of an inductively coupled plasma (ICP) torch for generating a plasma field into which a sample to be measured or analysed is introduced. In this form, the plasma vaporises and ionizes the sample so that ions from the sample can be introduced to a mass spectrometer for measurement/analysis (spectrometric analysis).
As the mass spectrometer requires a vacuum in which to operate, the extraction and transfer of ions from the plasma involves a fraction of the ions formed by the plasma passing through an aperture of approximately 1 mm in size provided in a sampler, and then through an aperture of approximately 0.4 mm in size provided in a skimmer (typically referred to as sampler and skimmer cones respectively).
Guidance of the ion beam through a mass spectrometer apparatus is generally controlled via shaped electric fields provided by suitably positioned electrodes which operate at controlled voltages. Arrangements of this type are normally referred to as ion optics systems.
A typical example of a well known ion optics system is that described in U.S. Pat. No. 6,614,021 (to Varian Australia Pty Ltd). However, although the arrangement described in US'021 operates sufficiently, there are some deficiencies which limit its measurement sensitivity at some ion energy levels.